Hydrogen peroxide induces intracellular calcium oscillations in human aortic endothelial cells.
BACKGROUND
Because the vascular endothelium is exposed to oxidant stress resulting from ischemia/reperfusion and from the products of polymorphonuclear leukocytes or monocytes, studies were performed to examine the effect of hydrogen peroxide (1 micromol/L to 10 mmol/L) on endothelial Ca2+ signaling.


RESULTS
At low concentrations (1 to 10 micromol/L), hydrogen peroxide did not affect intracellular Ca2+ concentration in subconfluent, indo 1-loaded human aortic endothelial monolayers. At a concentration of 100 micromol/L hydrogen peroxide, intracellular free Ca2+ gradually increased from 125.3+/-6.8 to 286.3+/-19.9 nmol/L over 4.2+/-0.9 minutes before repetitive Ca2+ oscillations were observed, consisting of an initial large, transient spike of approximately 1 micromol/L followed by several spikes of decreasing amplitudes at a frequency of 0.7+/-0.1 min-1 over 12.0+/-1.1 minutes. After these oscillations, intracellular Ca2+ reached a plateau of 543.4+/-64.0 nmol/L, which was maintained above baseline levels for >5 minutes and then partially reversible on washout of hydrogen peroxide in most monolayers. Intracellular Ca2+ oscillations were typically observed when monolayers were exposed to 100 to 500 micromol/L hydrogen peroxide. Higher concentrations of hydrogen peroxide (1 and 10 mmol/L) increased intracellular Ca2+ but only rarely (2 of 6 monolayers at 1 mmol/L) or never (at 10 mmol/L) stimulated intracellular Ca2+ oscillations. Removal of Ca2+ from the buffer either before hydrogen peroxide stimulation or during an established response did not block intracellular Ca2+ oscillations in response to 100 micromol/L hydrogen peroxide, but prior depletion of an intracellular Ca2+ store with either caffeine, histamine, or thapsigargin abolished Ca2+ oscillations.


CONCLUSIONS
Hydrogen peroxide induces concentration-dependent intracellular Ca2+ oscillations in human endothelial cells, which results from release of an endoplasmic reticulum Ca2+ store. Because oxidant production appears to occur in the micromolar range in the postischemic/anoxic endothelium and is associated with impaired endothelium-dependent relaxation, the effects of micromolar concentrations of hydrogen peroxide on endothelial Ca2+ signaling described in the present study may be important in the pathogenesis of postischemic endothelial dysfunction.
Hu
Q
Q
Department of Medicine, Johns Hopkins Bayview Medical Center, Johns Hopkins University School of Medicine, Baltimore, Md 21224-2780, USA.
Corda
S
S
Zweier
J L
JL
Capogrossi
M C
MC
Ziegelstein
R C
RC
D001011:Aorta / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D002021:Buffers; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D003600:Cytosol / Q000502:physiology; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D005110:Extracellular Space / Q000502:physiology; D006632:Histamine / Q000494:pharmacology; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D016877:Oxidants / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
D002021:Buffers; D016877:Oxidants; D006632:Histamine; D006861:Hydrogen Peroxide; D002118:Calcium